handbook-gas-shielding-18.html
AGA CW Handbook A4_32130-UK
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19 the effect of
shielding
gas
on productivity stainless steels in the mag welding of stainless steels, a small amount of an oxidising component (1–2% co 2 ) must be added to the argon-based shielding gas in order to stabilise the arc and minimise spatter. however, an inert shielding gas should be chosen for the welding of some high- alloy stainless steels, such as super-duplex and austenitic high-alloy stainless steels, if you wish to fully utilise the corrosion resistance characteristics of these steel grades. we recommend using the mison ® ar shielding gas instead of pure argon (which causes an unstable arc with a lot of spatter generation). in addition to argon, it contains 0.03% nitrogen monoxide, which is sufficient to stabilise the arc without mentionable oxide formation. the amount of post-weld finishing work is reduced which, in turn, improves the productivity of welding. 4.3.4 mig soldering when thin or metal-coated sheet metal is mig soldered, it is important to achieve an arc generating only a little heat in order not to melt the base material
(during soldering, only the filler material should melt). the arc must be stable in order to avoid spatter and porosity. pure argon as the shielding gas results in an unstable arc. different argon mixtures do provide a stable arc, but too much heat is gener- ated. the nitrogen monoxide contained in the mison ® ar shielding gas (ar+0.03% no) is enough to stabilise the arc while keeping heat generation low. experience from the automotive industry shows that the repair costs of solders are reduced by as much as 70% when pure argon is replaced with the mison ® ar shielding gas. the solder quality is also improved. the share of large spatter which weld easily onto surfaces of the total amount of spatter as the co2 content of the shielding gas changes. 4.3.5 adding helium or hydrogen by adding helium or hydrogen to a shielding gas, heat transfer to the weld is increased and the welding speed can be increased. examples of shielding gases containing helium are mison ® 2he, mison ® n2, mison ® he30, varigon ® he50 and varigon ® he70. these shielding gases provide a wider weld, wider penetration and enable a higher welding speed. when hydrogen is added to a shielding gas, the heat transfer to the weld increases and the arc becomes more focused, providing more pen- etration. the mison ® h2 shielding gas designed for the tig welding of austenitic stainless steels contains 2% hydrogen. the result is a higher welding speed, better penetration and a smoother fusion between the weld and the base material. the weld also becomes less oxidised and productivity is improved due to the reduced post-weld finishing work required. for more information on mison ® shielding gases, see chapter 10. the effects of the different shielding gas components are described in more detail in chapter 1. 4.4 filler material and shielding gas the general starting point of choosing the filler material is to use a filler material with the same chemical composition and strength as the base material. there are, naturally, numerous exceptions to this. the guide- books of the material and filler material suppliers contain information on which filler materials are suited to different base materials. the wire type can usually be chosen from either solid wire or cored wire (flux or metal cored). solid wires are used the most. using cored wire is benefi- cial in some applications. by choosing the right combination of filler material and shielding gas, the productivity of welding can be increased as a result of the higher welding speed and/or higher deposition rate. the appearance of the weld is also improved due to less spatter and surface oxides, and the smoother fusion of the weld and the base material. this reduces the amount of post-weld finishing work needed and increases productivity. the share of large spatter which weld easily onto surfaces of the total amount of spatter as the co2 content of the shielding gas changes 10 20 30 40 50 60 70 80 100 0 20 40 60 80 100 % carbon dioxide in argon share of large spatter
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